A cold-cathode discharge lamp used as a light source for backlighting of a liquid crystal display is configured such that cylindrical or plate metal is provided as an electrode in a lighting tube, which has a phosphor applied onto the inner surface of a glass tube, mercury and the like is contained therein, and the phosphor is excited by ultraviolet radiation that is generated in the lighting tube by discharge to provide visible radiation.
As to such a cold-cathode discharge lamp, a variety of studies on miniaturization, a smaller diameter, higher luminance, and a longer lifetime have been conducted in response to diversity of liquid crystal displays. For example, Japanese Patent Laid-Open No. 4-137429 proposes a cold-cathode discharge lamp, in which in order to reduce mercury consumed by sputtering in a lamp, a cylindrical electrode has an inner surface formed by a conductor and an outer surface formed by an insulator such that negative glow discharge does not circulate the outer circumferential surface of the cylindrical electrode.
In the cold-cathode discharge lamp configured thus, although it is possible to suppress blackening and consumption of mercury that are caused by sputtering materials on a tube inner wall, in the case of a large-current region demanding high luminance, negative glow discharge moves beyond the outside surface of the cylindrical electrode, which is formed by an insulator, to an internal lead-in wire. In such a state, the lead-in wire, which is drawn into a lighting tube to connect the cylindrical electrode and an external power supply and to hermetically seal the lighting tube, is less resistant to sputtering as compared with the cylindrical electrode. Thus, more sputtering materials are generated by increased sputtering on the lead-in wire, and mercury is consumed in the lamp, thereby interfering with a longer lifetime for the cold-cathode discharge lamp.
The present invention has as its object the provision of a cold-cathode discharge lamp which can solve the above-mentioned problem. The cold-cathode discharge lamp can suppress sputtering on a lead-in wire to achieve a longer lifetime.